FIELD OF THE INVENTION
The invention relates to a three-phase matrix converter for single-stage conversion of AC voltages of predetermined amplitude and frequency into AC voltages of any amplitude and frequency, having four-segment switches as main switches which are combined into three switch groups. The invention also relates to a method for operating the three-phase matrix converter.
The invention can be used, for example, for controlled-speed industrial drives using asynchronous or synchronous motors.
A three-phase matrix converter for single-stage power conversion of a three-phase AC voltage of specific predetermined amplitude and predetermined frequency into a three-phase AC voltage of variable amplitude and variable frequency is an alternative to hard and soft switching converters with a DC intermediate circuit (see, for example, a paper by M. G .B. Venturini and A. Alesina, entitled "Intrinsic Amplitude Limits and Optimum Design of 9-Switches Direct PWM-AC-AC Converters", in Conf. Rec. IEEE-PESC, 1988, pp. 1284-1291). The terms hard and soft switching converters in such a context relate to converters having switching processes (commutation processes) during which a respective relatively large or small amount of power loss is produced. The further development of the matrix converter is characterized by the implementation of space vector modulation, the use of the matrix converter in drives with field orientation and the use of backward turn-off IGBTs in the necessary four-quadrant switches.
The matrix converter has various advantages over conventional, hard switching PWM rectifier/DC intermediate circuit/invertor structures, for example the fact that the matrix converter does not require any capacitance in the intermediate circuit because of its single-stage power conversion. In addition, it produces lower losses than the comparable structure with a DC intermediate circuit since the commutation voltage of the matrix converter is considerably lower than that of the conventional converter with a DC intermediate circuit. Although the converter with a DC intermediate circuit requires only 24 power semiconductors (for example 12 IGBTs and 12 diodes) and the matrix converter requires 36 semiconductors (for example 18 IGBTs and 18 diodes), the installed total switch capacity for both converters generally the same because it is possible to reduce the rated currents of the switches in the matrix converter by a third.
However, the substantial switching losses limit the maximum switching frequency of hard switching converters in general to about 10 to 25 kHz in the medium power range if, for example, IGBTs are used. Increased fall and tail times with high-voltage power semiconductor components, such as GTOs, IGBTs and MCTs, exacerbate that effect even further in high-power applications, which leads either to highly voluminous and very expensive filter components or to higher motor losses in a drive used as a load.